Superconductivity above 200 K discovered in superhydrides of calcium

Abstract

Searching for superconductivity with Tc near room temperature is of great interest both for fundamental science & many potential applications. Here we report the experimental discovery of superconductivity with maximum critical temperature (Tc) above 210 K in calcium superhydrides, the new alkali earth hydrides experimentally showing superconductivity above 200 K in addition to sulfur hydride & rare-earth hydride system. The materials are synthesized at the synergetic conditions of 160~190 GPa and ~2000 K using diamond anvil cell combined with in-situ laser heating technique. The superconductivity was studied through in-situ high pressure electric conductance measurements in an applied magnetic field for the sample quenched from high temperature while maintained at high pressures. The upper critical field Hc(0) was estimated to be ~268 T while the GL coherent length is ~11 Å. The in-situ synchrotron X-ray diffraction measurements suggest that the synthesized calcium hydrides are primarily composed of CaH6 while there may also exist other calcium hydrides with different hydrogen contents.

Giant enhancement of superconducting critical temperature in substitutional alloy (La,Ce)H9

“…Meanwhile, inspired by the prediction of high-temperature superconductive CaH 6 15 , extensive ensuing studies have established a large family of clathrate superhydrides, including CaH 6 16 , 17 , YH 6 18 , YH 9 19 , 20 , CeH 9 21 – 23 , CeH 10 21 , and LaH 10 9 , 10 , which comprise an array of distinct hydrogen cages anchored at the center by a variety of metal atoms. The diverse structural and compositional forms of these binary compounds offer a platform for exploring material parameters to optimize the energetic and superconducting states.…”

Evidence Against Superconductivity in Flux Trapping Experiments on Hydrides Under High Pressure

“…Following the paper "Conventional superconductivity at 203 kelvin at high pressures in the sulfur hydride system", published in 2015 [2], several other hydrogen rich materials under high pressure have been reported in recent years to be high-temperature superconductors based on observed drops in resistance versus temperature [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Many more such materials have been determined to be conventional high-temperature superconductors based on theoretical evidence [20][21][22][23][24][25].…”

Synthesis of Weaire–Phelan Barium Polyhydride

“…The hydrogen cages would present H−H distances significantly longer than those of molecular hydrogen. 3,13,14 Subsequent theoretical works predicted similar structural motifs in the rare-earth metal hydrides YH 6 (stable above 300 GPa) and LaH 10 (stable above 200 GPa). 15,16 From the theoretical predictions, hydrogen clathrate cages are motifs promoting superconducting properties.…”